Apparatus for fabricating composite ceramic members

ABSTRACT

Method and apparatus for fabrication of composite ceramic members having particular application for measuring oxygen activities in liquid sodium. The method involves the simultaneous deposition of ThO2: 15% Y2O3 on a sintered stabilized zirconia member by decomposition of gaseous ThCl4 and YCl3 and by reacting with oxygen gas. Means establish an electrical potential gradiant across the zirconia member whereby oxygen ions, from a source on one side of the member portion to be coated, is migrated to the opposite side where a reaction and said decomposition and deposition is effected.

United States Patent 1191 Roy et a1. Oct. 28, 1975 APPARATUS FORFABRICATING [56] References Cited COMPOSITE CERAMIC MEMBERS UNITEDSTATES PATENTS ['75] Inventors: Prodyot Roy, Saratoga; James L.2,363.781 11/1944 Ferguson 118/49 X Simpson, San Jose; Edward A.2,802,127 8/1957 Dobischek et =11. 118/49 x Aitken Danville all ofK0116! X 3,208,873 /1965 Ames et a1. ll8/49.l X [73] Assigneez TheUnited States of America as represented y the United States PrimaryExaminerM0rris Kaplan ReSefrch and Development Attorney, Agent, orFirmJohn A. Horan; F. A. Administration, Washington, D.C. Robertson; ECamahan [22] Filed: May 7, 1974 7 [21] Appl. N0.: 467,684 [5 1 ABSTRACT:

Method and apparatus for fabr1cat|on of composite Publlshed under theTrial Voluntary Protest ceramic members having particular applicationfor Program on January 28, 197 as document measuring oxygen activitiesin liquid sodium. The 7 method involves the simultaneous deposition ofThO Related U S ""App|icati0n Data 15% Y O on a sintered stabilizedzirconia member by [62] Division of Ser No 3O] 41' Oct 27 1972decomposition of gaseous ThCl, and YC1 and by reacting with oxygen gas.Means establish an electrical [52] U S Cl 118/49 118/49 X potentialgradiant across the zirconia member 13/12 whereby oxygen ions, from asource on one side of the [58] Fieid 49 I 49 5 member portion to becoated, is migrated to the opp0 site side where a reaction and saiddecomposition and deposition is effected.

6 Claims, 1 Drawing Figure APPARATUS FOR FABRICATING COMPOSITE CERAMICMEMBERS This is a division, of application Ser. No. 301,411, filed Oct.27, 1972.

BACKGROUND OF THE INVENTION The invention described herein was made inthe course of, or under, Contract No. AT(04-3)-189, Project AgreementNo. 15, with the United States Atomic Energy Commission.

This invention relates to the fabricationof fabrication of ceramicmembers, and more particularly to the simultaneous deposition of ThOpercent Y O on a sintered stabilized zirconia member.

To satisfy the continuing demand for new and better materials variousprocesses and apparatus have been developed in the art. Theco-deposition of selected materials on a substrate, thus providing addedcapabilities of satisfying the needs for new materials are exemplifiedby U.S. Pat. No. 3,268,362 issued Aug. 23, 1966, and No. 3,343,979issued Sept. 26, 1967. With the development of liquid metal as a coolantfor nuclear reactors additional requirements for materials which willwithstand the operating conditions have been imposed. For example,simple yet effective means for providing measurements of oxygenconcentration of liquid sodium in the liquid metal fast breeder reactorhas produced a need for materials capable of withstanding thetemperature and corrosion conditions imposed thereon, such a meanshaving been described and claimed in co-pending U.S. Pat. ApplicationSer. No. 306,976, filed Nov. 15, 1972, now U.S. Pat. No. 3,776,832,entitled Device For Measuring Oxygen Activity, which basically comprisesa composite ceramic member of stabilized zirconia coated with a thinlayer of thoria-yttria.

Conventional methods of fabrication of composite ceramics areco-extrusion, plasma spraying, and slip castings. All these processesreguire high temperature (1,900C) heat treatment for sintering of theceramics to attain an impervious state. Sintering of the compositematerials at a high temperature creates severe problems due todifferential thermal expansion of two different materials which causescracking during sintering operations.

SUMMARY OF THE INVENTION The present invention overcomes the problems ofthe prior art methods of fabricating composite ceramic members byeliminating the high temperature sintering and thus the crackingproblems associated therewith, while eliminating impurity contaminationduring processing and providing better control on the thickness of thelayers at fabricating costs lower than those of conventional methods.This is accomplished by a apparatus which involves the simultaneousdeposition of ThO 15% Y O on a sintered stabilized zirconia member bydecomposition of gaseous ThCl and YCl and by reacting with oxygen gas.

Therefore, it is an object of this invention to provide an apparatus forfabricating composite ceramic members.

A further object of the invention is to provide an apparatus forfabricating composite ceramic members by deposition of ThO z 15% Y O ona sintered stabilized zirconia member.

Another object of the invention is to provide an apparatus for makingcomposite ceramic members involving decomposition of gaseous ThCL, andYCl and by reacting with oxygen gas.

Another object of the invention is to provide an apparatus forsimultaneously depositing ThO 15% Y O on a sintered stabilized zirconiamember by decomposition of gaseous ThCl and YCl and by reacting withoxygen gas.

Other objects of the invention will become readily apparent from thefollowing description and accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE, partially incross-section, illustrates the novel apparatus for carrying out theinventive fabrication method.

DESCRIPTION OF THE INVENTION This invention is directed to an apparatusand method for producing composite ceramic members by the simultaneousdeposition of ThO 15% Y O on a sintered stabilized zirconia member bydecomposition of gaseous ThCL, and YCl and by reacting with oxygen gas.Members made in accordance with this invention have particularapplication in the measurement of oxygen concentration of liquid sodium,and the description will be directed toward the fabrication of a closedend ceramic tube utilized for such measurements, but it is not intendedto limit the invention to the specific configuration produced thereby orto the above-described application therefor, as the invention can beutilized for producing various configurations for numerous applications.

Basically, the invention consists of simultaneous deposition ofthoria-yttria (ThO 15%( O on a sintered stabilized zirconia tube, suchas zirconia-calcia (ZrO 15% CaO), by decomposition of gaseous ThCl, andYCl by reacting it with oxygen gas by the following reaction:

ThCh 02%,) Z ThO 2 Y Cl At about I,OOOC, this type of gaseousdecomposition product will form a layer of homogeneous and theoreticallydense mixture of ThO and Y O on the zirconia substrate.

In order to deposit ThO and 0 on the outside surface of a zirconia tube,oxygen must be made available at the surface of the tube. This isaccomplished by migrating oxygen gas from inside the tube across thetube wall to the outside surface, as described in greater detailhereinafter.

Referring now to the drawing an embodiment of the novel apparatus forcarrying out the method of fabrication is illustrated and comprises abell jar 10 containing a static atmosphere indicated at 11 of a mixtureof gaseous chlorides (T hCl, and YCl in proper proportion, about aclosed-end tube or member 12 of stabilized zirconia (ZrO 15 percent CaO)positioned within bell jar 10 and having reduced diameter end portion 13extending from an opening 14 in the bell jar with an O- ring seal 15about opening 14 to prevent leakage of the gaseous chloride mixture 11from the bell jar 10. The oxygen gas required to deposit ThO and Y O onthe outer surface of the zirconia tube 12 is migrated through the wallsof tube 12 from an oxygen supply 15 extending into an interior chamberor cavity 16 of the tube 12. The oxygen gas reaching the outer surfaceof the tube will react instantly with the gaseous mixture 11 of ThCL,and YCl to form respective oxides on the surface of the tube. Since boththe stabilized zirconia tube 12 and the oxide layer of ThO 15% Y Oformed on the surface thereof are theoretically dense, moleculardiffusion of the oxygen gas through the tube wall will not take place.However, both of these ceramics are anionic conductors, hence O ions canbe migrated through the tube wall under an electrical potentialgradient. To accomplish this, the inside surface of the stabilizedzirconia tube 12 is coated with a thin conductive film 17 such as goldwhich will act as a cathode, while the outside of the tube 12 issurrounded by a grid cage 18 made of an electrical conductive material(e.g., an alloy of Th with 15% Y), the grid cage 18 being placed at adistance of approximately one centimeter from the outside surface oftube 12, and will act as an anode. Grid cage 18 is connected to anelectrical lead 19 from a variable d-c power supply 20, while conductivefilm 17 is connected via lead 21 to power supply 20. Bell jar isprovided with an insulative collar or member 22 through which electricalconnection between cage 18 and lead 19 extends. A voltmeter 23 ispositioned between leads 19 and 21 and in parallel with power supply 20,while an ammeter 24 is connected in lead 21 intermediate the conductivefilm 17 and the point of connection of voltmeter and lead 21. Thestabilized zirconia tube 12 is heated, for example, to the abovementioned temperature of about l,()O0C by a resistance heater 25positioned in the interior cavity 16 of the tube and is connected to anappropriate power supply, not shown, the temperature of conductive film17 being indicated by a thermocouple 26. Thus, a d-c potential will beapplied across the cathode (film 17) and the anode (grid cage 18)thereby providing an electrical potential gradient across tube 12 suchthat the oxygen gas from supply at the inside of the tube will enablethe oxygen ions to migrate across the tube walls to react with thegaseous chlorides of mixture 11 by the following mechanisms:

Grid Cage (Th metal? 4 c1" Th 'IhCl The amount of oxygen passing throughthe walls of tube 12 will be determined by measuring the currentindicated by ammeter 24, flowing through the tube wall. The rate ofoxygen migration, and consequently the rate of oxide film or layergrowth on the outside surface of tube 12 will be controlled by changingthe potential, indicated by voltmeter 24, across the tube.

Thus, the present invention provides a method and apparatus forproducing composite ceramics which has the following improvements overconventional processing techniques:

1. No high temperature 1,900C) sintering is required and thus thecracking problems due to differential thermal expansion of two differentceramics at high temperature is eliminated.

2. A better control on the thickness of the ceramic layers is provided.

3. Impurity contamination of the ceramics during processing (e.g.,grinding, heat treatment, etc.) is eliminated.

4. The cost of fabricating these types of ceramics is considerably lessthan conventional methods.

While a particular embodiment of the apparatus and specific materialshave been set forth to illustrate and describe the invention,modifications will become apparent to those skilled in this art, and itis intended to cover in the appended claims all such modifications ascome within the spirit and scope of the invention.

What we claim is:

1. An apparatus for fabricating composite ceramic members composed of astabilized zirconia member having a coating of ThO 15 percent Y O on atleast one surface thereof comprising: a container means within which anassociated tubular zirconia member to be coated is positioned; a closedend of said member extending through, and in sealing relation with, awall of said container; a mixture of gaseous ThCl and YCl contained insaid container means for contact with the outer surface of said member;anode means disposed within said container and spaced from at least aportion of said outer surface; cathode means disposed within said tubeand contacting at least a surface portion thereof opposite said portionof the outer surface; power supply means connected to said anode andcathode means for producing an electrical potential gradiant across thetubular wall portion between said surface portions; means for supplyingoxygen within said member; and means for heating said member wherebyions of oxygen migrate through said wall portion to effect said reactionand coating, anode means constructed to be positioned about and inspaced relation with the portion of an associated member to be coatedwhich is in contact with said gaseous mixture, cathode means constructedto be in contact with a portion opposite the first-mentioned portion ofan associated member to be coated, power supply means connected to saidcathode means and to said anode means for producing an electricalpotential gradient across an associated member to be coated, means forsupplying oxygen to the oxygen adjacent said cathode means, and meansfor heating an associated member to be coated.

2. The apparatus defined in claim 1, wherein said container meanscomprises a bell jar.

3. The apparatus defined in claim 1, wherein said anode means comprisesa grid cage and said cathode means comprises a conductive film on aninner portion of such an associated member.

4. The apparatus defined in claim 1, said member to be coated is asintered stabilized zirconia member ZrO CaO to be coated bydecomposition of gaseous ThCl and YCl by reacting with oxygen, whereinsaid container means comprises a bell jar, wherein said cathode meanscomprises a conductive film secured to an interior portion of saidmember, wherein said anode means comprises a grid cage, wherein saidpower supply means operatively connected to said cathode means and anodemeans for providing an electrical potential gradient across saidtube-like zirconia member comprises a dc power supply, wherein saidmeans for supplying oxygen di-

1. AN APPARATUS FOR FABRICATING COMPOSITE CERAMIC MEMBERS COMPOSED OF ASTABILIZED ZIRCONIA MEMBER HAVING A COATING OF THO2: 15 PERCENT Y2O3 ONAT LEAST ONE SURFACE THEREOF COMPRISING: A CONTAINER MEANS WITHIN WHICHAN ASSOCIATED TUBULAR ZIRCONIA MEMBER TO BE COATED IS POSITIONED, ACLOSED END OF SAID MEMBER EXTENDING THROUGH, AND IN SEALING RELATIONWITH, A WALL OF SAID CONTAINER MEANS FOR CONTACT WITH THE OUTERCONTAINED IN SAID CONTAINER MEANS FOR CONTAACT WITH THE OUTER SURFACE OFSAID MEMBER, ANODE MEANS DISPOSED WITHIN SAID CONTAINER AND SPACED FROMAT LEAST A PORTION OF SAID OUTER SURFACE, CATHODE MEANS DISPOSED WITHINSAID TUBE AND CONTACTING AT LEAST A SURFACE PORTION THEREOF OPPOSITESAID PORTION OF THE OUTER SURFACE, POWER SUPPLY MEANS CONNECTED TO SAIDANODE AND CATHODE MEANS FOR PRODUCING AN ELECTRICAL POTENTIAL GRADIANTACROSS THE TUBULAR WALL PORTION BETWEEN SAID SURFACE PORTIONS, MEANS FORSUPPLYING OXYGE WITHIN SAID MEMBER, AND MEANS FOR HEATING SAID MEMBERWHEREBY IONS OF OXYGEN MIGRATE THROUGH SAID WALL PORTION TO EFFECT SAIDREACTION AND COATING, ANODE MEANS CONSTRUCTED TO BE POSITIONED ABOUT ANDIN SPACED RELATION WITH THE PORTION OF AN ASSOCIATED MEMBER, TO BECOATED WHICH IS IN CONTACT WITH SAID GASEOUS MIXTURE, CATHODE MEANSCONSTRUCTED TO BE IN CONTACT WITH A PORTION OPPOSITE THE FIRST-MENTIONEDPORTION OF AN ASSOCIATED MEMBER TO BE COATED, POWER SUPPLY MEANSCONNECTED TO SAID CATHODE MEANS AND TO SAID ANODE MEANS FOR PRODUCING ANELECTRICAL POTENTIAL GRADIENT ACROSS AN ASSOCIATED MEMBER TO BE COATED,MEANS FOR SUPPORTING OXYGEN TO THE OXYGEN ADJACENT SAID CATHODE MEANS,AND MEANS FOR HEATING AN ASSOCIATED MEMBER TO BE COATED.
 2. Theapparatus defined in claim 1, wherein said container means comprises abell jar.
 3. The apparatus defined in claim 1, wherein said anode meanscomprises a grid cage and said cathode means comprises a conductive filmon an inner portion of such an associated member.
 4. The apparatusdefined in claim 1, said member to be coated is a sintered stabilizedzirconia member ZrO2:15 % CaO to be coated by decomposition of gaseousThCl4 and YCl3 by reacting with oxygen, wherein said container meanscomprises a bell jar, wherein said cathode means comprises a conductivefilm secured to an interior portion of said member, wherein said anodemeans comprises a grid cage, wherein said power supply means operativelyconnected to said cathode means and anode means for providing anelectrical potential gradient across said tube-like zirconia membercomprises a d-c power supply, wherein said means for supplying oxygendirects oxygen into the interior portion of said member, and whereinsaid means for heating said member comprises a resistance heaterpositioned within said interior portion of said member.
 5. The apparatusdefined in claim 1, additionally including a thermocouple meanspositioned in contact with said cathode means.
 6. The apparatus of claim1, wherein said cathode comprises a coating on said member defining anannulus and said anode comprises a grid member configured about an axiscommon to said cathode.